Treatment of lead



April 1, 1958 D. R. BLAsKET'r TREATMENT oF LEAD 2 Sheets-Sheet 1 Filed April l1. 1955 LEAD `BULLION CONTAINING BIMUTH April 1, 1958 b. R. BLAsl-{ETT TREATMENT oF LEADv 2 sheets-sheet 2 v Filed April 1l, 1955 United States Patent@ e TREATMENT OF LEAD Donald Reginald Blaskett, Port Pirie, South Australia, Australia, assigner to The Broken Hill Associated Smelters Proprietary Limited, Melbourne, Australia, a company of Victoria Application April 11V, 1955, Serial No. 500,597

Claims priority, application Australia April' 28, 1954 7 Claims. (Cl. 2041-66) Another known method of debismuthising lead involvesl the treatment of the molten metalwith potassium and magnesium. The lead so Vtreated contains residual mag.- nesium and potassium, the magnesium being subsequently separated as magnesium oxide after which the potassium is removed in the form of the hydroxide.

Accordingly the object of this invention is to provide an improved method of -addingalkali metal to bismuthlead for the purpose of refining the latter.

The invention includes the method of removing sodium or potassium from debismuthised lead comprising subjecting the moltenhydroxide of the alkali metal to electrolysis using the molten lead alloy as the anode and molten lead as the cathode, whereby the alkali metal passes into thek electrolyte from the anode and is simultaneously deposited on the cathode and mixing the cathode lead, thus produced, with additional bismuth-lead preparatory to subjecting it to a debismuthising treatment.

The ,metal may be treated in successive batches, or alternatively both the anode and the cathode metals may flow continuously through the electrolytic cell in which case they may pass therethrough in parallel streams which How in opposite directions. f

A salient feature of the preferred form of the invention resides in using molten lead containing the alkali metal to form both the anode and the cathode whereby the proportion thereof in the cathodic body or stream is increased as that of the anodic body or stream is depleted, the enriched alkali-metal lead alloy thus produced The quantities of metal used to form the anodel and cathode are not necessarily the same as either may be greater than the other according to requirements. Moreover,it may be advantageous for the reason hereinafter explained to return some of the debismuthisedV lead for admixture with additional lead without subjecting it to the aforesaid electrolytic treatment.

A further feature of the invention resides in incorporating additional alkali metal in the lead by the electrolysis of the hydroxide either in the same or in a separate cell.

In the drawings:

Figure l is a flow sheet showing the invention applied to the removal of sodium from lead bullion and the re-use of the recovered sodium for the refining of additional lead,

. 2,829,093 Patented Apr. l., Vi958 electrolytic cell,

Figure 3 is a view in plan of the cell,

Figure 4 is a flow sheet of a modified process,

Figure 5 is a perspective view of an alternative form of electrode, p

.Figure 6 is a diagrammatic view in sectional elevation of an electrolytic cell incorporating electrodes of the kind shown in Figure 5 and showing an associated debismuthising unit,

v Figure 7 is a view in sectional elevation taken on the line '7-7 of Figure 6, and

Figure 8 is a perspective view of still another type of electrode.

The flow sheet-Figure l-shows one application of the invention to the treatment of lead bullion containing bismuth the latter being initially subjected to a suitable treatment wherein sodium is used to remove the bismuth. This debismuthising treatment does not form a part of the present invention as suitable methods, suchas those disclosed in United States patent specification No. 2,365,177, No. 2,402,316 and No. 2,507,096, are already known.

The debismuthised lead containing sodium is directed into a holding vessel and is delivered from the latter into two trough-shaped electrodes l0 and 11 respectively within an electrolytic cell l2 containing molten caustic soda as the electrolyte, the latter being maintained at a suit# able temperature, somewhat above the melting point of lead, e. g. a temperature of about 330-340 C. 'The cell may be operated either intermittently or continuously according to whether it is desired to treat the lead in successive batches or continuously.

in the case of a batch treatment a suitable potential which, for lead containing about 2% sodium, usually various from about 0.8 volt at the commencement of Vthe' operation, to about 1.2 volts at the end thereof, is maintained between the electrodes, as a result of which sodium is deposited on and incorporated in the molten lead cathode, while simultaneously sodium passes into the elec'- trolyte from the molten lead anode. Consequently as the operation proceeds, the proportion of sodium in the anode metal is progressively decreased while that in the cathode is progressively increased and the operation is preferably continued until the anode metal is substantially completely free of sodium at which time an equal quantity of sodium has been added to the cathode lead.

Thus, if the lead initially contains say 2% of sodium and equal quantities thereof are used to form the anode and cathode, the cathodic lead containsV about 4% of sodium at the conclusion of the electrolytic treatment while the anodic leadis substantially free of sodium.

When the anode lead is substantially completely depleted of sodium, the voltage required rises sharply from about l.2 volts to about 2.5 volts and thus provides anse ful indication of the completion oi the process.

The current efficiency is high with an ,average poten-y tial dilierence of about l volt and with a current density of about 500 to 1000 amps. per square foot of cathode surface.

The electrolytic cell l2 therefore serves as a sodium exchanger in that, in effect, the sodium is transferred therein from the anode to the cathode.

At the conclusion of the electrolytic treatment the sodium free anode lead is discharged from the system while the sodium enriched cathode lead is returned as shown for admixture with additional lead bullion in advanceA of the debismuthising stage so as to provide the sodium necessary for the debismuthising treatment thereof. ,Thus

if the returned 4% sodium blead is mixed with an equal.. 'l quantity of bullion, the mixture contains 2% of sodium.

However, it is not necessary to use equal quantities of the bismuth free sodium-lead to form the anode and cathode as the quantity used to form either electrode may be greater than thatused Afor the other, according to requirements. A u

Thus if it is desired to produce a sodium leadV having a particular sodium content, the quantities used to form the anode and cathode are such as to produce the required alloy. For example in order to produce an alloy containing 6% of sodium from lead which initially contains 2%, the quantity of lead used for the cathode would be one half` of the quantity used to form the anode and so on. Sodium lead containing up to about 10% sodium r may readily be produced in this way.

It may not be necessary to pass all of the recirculated lead through the electrolytic cell. Thus as shown by the broken line DR in Figure l, some of the debismuthised lead may be returned immediately vto the debismuthising stage.

For example the debismuthising apparatus may operate at maximum etliciency when the entering lead contains say 0.005 bismuth and 2% sodium, in which case if the new lead contains 0.01% bismuth, the desired result would be obtained if equalquantities of the debismuthised lead are used to form the anode and the cathode. In these circumstances, the nal cathode lead would contain 4% sodium and so when mixed with an equal quantity of new lead containing 0.01% bismuth, it would produce the required alloy containing 0.005% bismuth and 2% sodium.

If, however, the new lead contained 0.02% bismuth, it would be necessary lto mix it with three times the quantity of debismuthised lead in order to reduce the bismuth content of the mixture to the required value of 0.005%. As it would not be necessary to use all of this returned lead to carry the sodium recovered in the electrolytic cell, a suitable proportion could be returned directly as indicated by the aforesaid broken line DR.

More particularly, one quarter of the debismuthised leadwould be used in the described circumstances to form vthe anode and if an equal quantity were used to form the cathode, the remaining one half of the debismuthised lead containing 2% sodium would be returned direct to the debismuthising stage without passing through the electrolytic cell. contain 4% sodium and when mixed with an equal quantity of fresh lead, the mixture would contain the required 2% of sodium.

It `willi ofcourse beapparent that when the electrolytic operation is carried out intermittently, the quantity of new lead entering the system must on the average be equal to sodium free anode lead which is discharged while if Figure l is regarded as depicting a continuous treatment, the rate of inow of fresh lead would be equal to the rate of discharge of bismuth and sodium free anode lead.

Consequently the sodium in the system recirculates through the debismuthising stage and at least partly through the sodium exchanger cell as shown in the diagram.

However, some losses of sodium inevitably occur during the debismuthising stage and it is necessary to make good these losses. When the said electrolytic cell is used for the treatment of successive batches of lead, this make-up sodium may be provided by increasing the voltage of the cell to about 3-4 volts after substantially all of the sodium has been removed from the anode lead whereby additional sodium is deposited on the cathode lead by the electrolytic reduction of the fused caustic soda. This operation, serves also to remove any residue of sodium in the anode lead. Alternatively and as hereinafter further explained, with particular reference to a continuous operation, the additional sodium required may be supplied by a separate electrolytic treatment.

Figures 2 and 3 show somewhat diagrammatically a suitableformof electrolytic cell for the treatment of the The cathode lead would metal in batches. This cell comprises an elongated cast iron pan `12 which is open at the top and is set in brickwork 13 whereby it may be heated by gas or oil burners (not shown).

The anode 10 and cathode 11 each consists of an elongated steel or cast iron trough of semi-circular shape in cross-section arranged in the same horizontal plane within the pan. The troughs may be supported on insulating refractory material 14 at the bottom of the pan or alternatively they may be suspended from overhead supports (not shown).

The electrode troughs are completely submerged in the electrolyte 15 with their adjacent edges disposed say about two inches apart.

Figure 4 is a flow sheet showing a modified process in which molten lead ows continuously into and through the cell 12 in the form of anodic and cathodic streams and are continuously discharged therefrom. Thus the anodic lead is progressively depleted of sodium as it passes through the cell while the cathodic stream is progressive ly enriched in sodium. The anodic and cathodic streams may ow through opposed electrode troughs or channels 10 and 11 respectively arranged substantially in lateral opposition as shown in Figures 2 and 3 in which case the streams preferably pass in couutertiow as indicated in Figure 4.

The make-up sodium is added to the cathodic stream by the electrolysis of caustic soda in a separate cell 17 provided with an anode trough or channel 18 and a cathode trough or channel 19 and it will be noted that the sodium free anode stream from the` sodium exchange cell 12 is directed into the make-up cell 17 to serve as the anode therein.

It will be apparent that it is necessary for the anode and cathode streams to be electrically insulated and also that it is necessary to interrupt the .anode streams between the cells 12 and 17 in order that different voltages may be maintained therein. This result may be achieved for example by causing the anodic stream to break into separate drops when passing over weirs or from discharge nozzles located at the positions designated 20, 2l and 22 and the cathode stream may be similarly interrupted. Alternatively insulated holding vessels (not indicated) for the anode lead may be arranged at each side of each electrolytic cell.

In lieu of causing the molten metal to flow horizontally through the cells 12 and 17 it may alternatively and advantageously pass vertically therethrough whereby the electrode area for a given floor space may be increased.

Thus one suitable construction of electrode shown in Figure 5 comprises a series of horizontal troughs 24 arranged one above the other and spaced a suitable distance apart with their ends secured to vertical end members 25. Each trough 24 may conveniently consist of a length of angle section steel as shown and is provided below the top thereof with a series of drain holes or notches 27 whereby the molten metal is continuously discharged therefrom into the next trough of the series.

One construction of cell incorporating multiple electrodes of the kind shown in Figure 5 is illustrated in Figures 6 and 7 in association with a debismuthising tower 30.

A plurality of alternately arranged anodes 10 andfcathodes 11 are arranged within the cell and the molten sodium lead passes into the upper trough 24 of each electrode from a common superposed feed trough 31 fitted with a plurality of adjustable discharge valves 32--onc for each electrode.

The discharge nozzle of each valve is located some 7 or more inches above the uppermost trough 24 of the rcspective electrode in order that each stream of metal will break up into drops and so obviate any serious short circuting.

The molten metal thus continuously delivered tothe uppermost trough 24 of each electrode is continuously discharged therefrom at the same rate through the openings 27 to enter the next trough in the series until it is finally discharged from the lowermost trough and descends in the form of separate drops into a corresponding collecting well 33 or 34 in the bottom of the cell. Thus the molten metal in the wells 33 and 34 is insulated from the electrodes.

The cathode metal which is collected in the wells 34 is continuously discharged therefrom into a common collecting pot 35 through corresponding U traps 36 while similarly the anode metal collected in the wells33 is discharged therefrom through U traps 37 into a launder 38.

The metal discharged from the debismuthising tower 30 is also delivered by a pipe 39 into the pot 35 and the molten metal is continuously discharged from the latter, by a centrifugal pump 40 driven by an electric motor 41, into the feed trough 31 which has its discharge end projecting above the top of the tower 30.

Thus any of the recirculated metal which is not discharged through the valves 32 into the electrodes is returned directly to the debismuthising stage as previously described. The fresh lead to be treated passes continuously into the tower 30`through a pipe 42.

Figure 8 shows another form of vertical electrode comprising a steel plate 43 having a horizontal distributing pipe 44 4for the molten sodium lead alloy welded to its upper edge. This pipe is provided with a series of discharge holes or slits 45 disposed close to the surface of the plate so that the molten metal is continuously supplied thereto. As the molten sodium-lead alloy wets the surface of the steel plate, it flows continuously downwards over the latter in the form of a thin film and is nally discharged into a corresponding well arranged as shown in Figures 6 and 7. l

While the preceding particular description relates only to the treatment of bismuth-lead with sodium, it will be evident that potassium may alternatively be employed, in which case, potassium hydroxide is used as the electrolyte. Thus according to this form of the invention, the potassium-enriched cathode lead may be returned for admixture with additional lead containing bismuth as described and illustrated in relation to the treatment of sodium lead. f

I claim:

1. The method of refining lead containing bismuth comprising mixing the molten bismuth lead with molten lead which is substantially free of bismuth, but which contains an alkali metal selected from the group consisting of sodium and potassium, subjecting the mixture to a debismuthising treatment, subjecting molten hydroxide of the alkali metal to electrolysis between an anode and a cathode each formed of molten debismuthised lead whereby additional alkali metal is deposited on and incorporated in lthe cathode while the content of the alkali metal in the anode is reduced, and mixing lead, thus enriched in the alkali metal, with additional bismuth lead for a further cycle of operations.

2. The method of refining lead containing bismuth comprising mixing the molten bismuth lead with 'molten lead which is substantially free of bismuth, but which contains an alkali metal selected from the group consisting of sodium and potassium, subjecting the mixture to a debismuthising treatment, subjecting molten hydroxide of the alkali metal to electrolysis between electrodes comlead which is substantially free of bismuth, but which,

contains an alkali metal selected from the group consisting of sodium and potassium, subjecting the mixture to a debismuthising treatment, electrolysing molten hydroxide of the alkali metal, between electrodes composed of batches of molten debismuthised lead and continuing the operation until the anode lead is substantially free of the alkali metal and the cathode lead is correspondingly enriched therein and mixing lead thus enriched in the alkali metal with additional bismuth lead for a further cycle of operations.

4. The method according to claim 3 including the step of incorporating additional alkali metal in the said cathode lead by the electrolytic reduction of molten hydroxide of the alkali metal. l

5. The method of refining lead containing bismuth comprising mixing the molten bismuth lead with molten lead which is substantially free of bismuth, but which contains an alkali metal selected from the group consisting of sodium and potassium, subjecting the mixture to a debismuthising treatment, electrolysing molten hydroxide of the alkali metal between electrodes constituted by streams of molten debismuthised lead which streams pass substantially continuously into and through the electrolyte at a rate such that the anode metal discharged from the electrolyte is substantially free of alkali metal while the cathode metal is correspondingly enriched thereinV and `mixing thus enriched lead with additional bismuth lead molten lead containing an alkali metal previously added electrolytically as hereinafter set forth in this claim, separating bismuth from the mixture and subsequently subjecting the molten hydroxide of the alkali metal to electrolysis using, as anode, the molten debismuthised lead which contains residual alkali metal, and using molteny lead as cathode whereby alkali'metal passes from the anode lead into the electrolyte and is simultaneously deposited on and incorporated in the cathode lead and mixing the resultant cathode lead containing alkali metal with fresh molten bismuth-lead alloy for a further cycle of References Cited in the le of this patent UNITED STATES PATENTS 789,721 Decker May 16, 1905 801,199 Ashcroft Oct. 10, 1905 1,447,143 Mathesius Feb. 27, 1923 2,521,217 Heberlein et al. Sept. 5, 1950 2,598,228 Cox May 27, 1952 

1. THE METHOD OF REFINING LEAD CONTAINING BISMUTH COMPRISING MIXING THE MOLTEN BISMUTH LEAD WITH MOLTEN LEAD WHICH IS SUBSTANTIALLY FREE OF BISMUTH, BUT WHICH CONTAINS AN ALKALI METAL SELECTED FROM THE GROUP CONSISTING OF SODIUM POTASSIUM, SUBJECTING THE MIXTURE TO A DEBISMUTHISING TREATMENT, SUBJECTING MOLTEN HYDROXIDE OF THE ALKALI METAL TO ELECTROLYSIS BETWEEN AN ANODE AND A CATHODE EACH FORMED OF MOLTEN DEBISMUTHISED LEAD WHEREBY ADDITIONAL ALKALI METAL IS DEPOSITED ON AND INCORPORATED IN THE CATHODE WHILE THE CONTENT OF THE ALKALI METAL IN THE ANODE IS REDUCED, AND MIXING LEAD, THUS ENRICHED IN THE ALKALI METAL, WITH ADDITIONAL BISMUTH LEAD FOR A FURTHER CYCLE OF OPERATIONS. 